A normal functioning nervous system depends upon the ability of neurons to recognize and synapse with their appropriate target cells during development. Although the cellular events involved in this type of cell interaction have been well described in both vertebrates and invertebrates, the underlying molecular mechanisms are poorly understood. Our long-term goal in this project is to understand the molecular basis of these neuronal recognition events. The approach we have taken is to use the genetics of Drosophila to identify genes and gene products that are involved in neuronal recognition. To this end, we have isolated mutations that alter the synaptic connections between identified neurons within a simple neuronal circuit. One of these mutations, called bendless (ben), appears to alter the recognition event leading to proper connectivity between two well characterized neurons of the circuit, the giant fiber and one of its post-synaptic targets, the TTM motoneuron. We have mapped the genomic location of the ben gene on a molecular walk through the region, and propose both to identify the ben transcription unit and to use molecular genetic and transformation techniques to study the role of the ben gene product in the target recognition process. We will determine which cells require ben function, and also misexpress the gene during development. We expect that these experiments will provide us with a better understanding of the target recognition process and its molecular basis, not only in Drosophila, but in higher vertebrates as well.